[SFTP-v3] Allow to set preferred algorithms

docker-compose.yml

@@ -29,6 +29,16 @@ services:
       - ./test_files/sftp/id_rsa.pub:/home/bar/.ssh/keys/id_rsa.pub
     ports:
       - "2222:22"
+  sftp_eddsa_only:
+    container_name: sftp_eddsa_only
+    restart: always
+    image: atmoz/sftp
+    volumes:
+      - ./test_files/sftp/users.conf:/etc/sftp/users.conf
+      - ./test_files/sftp/sshd_custom_configs.sh:/etc/sftp.d/sshd_custom_configs.sh
+      - ./test_files/sftp/ssh_host_ed25519_key:/etc/ssh/ssh_host_ed25519_key
+    ports:
+      - "2223:22"
   ftp:
     container_name: ftp
     restart: always

src/PhpseclibV3/SftpConnectionProvider.php

@@ -78,6 +78,11 @@ class SftpConnectionProvider implements ConnectionProvider
      */
     private $maxTries;
 
+    /**
+     * @var array
+     */
+    private $preferredAlgorithms;
+
     public function __construct(
         string $host,
         string $username,
@@ -89,7 +94,8 @@ public function __construct(
         int $timeout = 10,
         int $maxTries = 4,
         string $hostFingerprint = null,
-        ConnectivityChecker $connectivityChecker = null
+        ConnectivityChecker $connectivityChecker = null,
+        array $preferredAlgorithms = []
     ) {
         $this->host = $host;
         $this->username = $username;
@@ -102,6 +108,7 @@ public function __construct(
         $this->hostFingerprint = $hostFingerprint;
         $this->connectivityChecker = $connectivityChecker ?: new SimpleConnectivityChecker();
         $this->maxTries = $maxTries;
+        $this->preferredAlgorithms = $preferredAlgorithms;
     }
 
     public function provideConnection(): SFTP
@@ -131,6 +138,7 @@ public function provideConnection(): SFTP
     private function setupConnection(): SFTP
     {
         $connection = new SFTP($this->host, $this->port, $this->timeout);
+        $connection->setPreferredAlgorithms($this->preferredAlgorithms);
         $connection->disableStatCache();
 
         try {
@@ -190,7 +198,8 @@ public static function fromArray(array $options): SftpConnectionProvider
             $options['timeout'] ?? 10,
             $options['maxTries'] ?? 4,
             $options['hostFingerprint'] ?? null,
-            $options['connectivityChecker'] ?? null
+            $options['connectivityChecker'] ?? null,
+            $options['preferredAlgorithms'] ?? [],
         );
     }
 

src/PhpseclibV3/SftpConnectionProviderTest.php

@@ -4,6 +4,7 @@
 
 namespace League\Flysystem\PhpseclibV3;
 
+use phpseclib3\Exception\NoSupportedAlgorithmsException;
 use phpseclib3\Net\SFTP;
 use PHPUnit\Framework\TestCase;
 
@@ -21,6 +22,8 @@
  */
 class SftpConnectionProviderTest extends TestCase
 {
+    const KEX_ACCEPTED_BY_DEFAULT_OPENSSH_BUT_DISABLED_IN_EDDSA_ONLY = 'diffie-hellman-group14-sha256';
+
     public static function setUpBeforeClass(): void
     {
         if ( ! class_exists(SFTP::class)) {
@@ -241,6 +244,60 @@ public function providing_an_invalid_password(): void
         $provider->provideConnection();
     }
 
+    /**
+     * @test
+     */
+    public function authenticate_with_supported_preferred_kex_algorithm_succedes(): void
+    {
+        $provider = SftpConnectionProvider::fromArray(
+            [
+                'host' => 'localhost',
+                'username' => 'foo',
+                'password' => 'pass',
+                'port' => 2222,
+                'preferredAlgorithms' => [
+                    'kex' => [self::KEX_ACCEPTED_BY_DEFAULT_OPENSSH_BUT_DISABLED_IN_EDDSA_ONLY],
+                ],
+            ]
+        );
+        $this->assertInstanceOf(SFTP::class, $provider->provideConnection());
+
+        $provider = SftpConnectionProvider::fromArray(
+            [
+                'host' => 'localhost',
+                'username' => 'foo',
+                'password' => 'pass',
+                'port' => 2223,
+                'preferredAlgorithms' => [
+                    'kex' => ['curve25519-sha256'],
+                ],
+            ]
+        );
+        $provider->provideConnection();
+        $this->assertInstanceOf(SFTP::class, $provider->provideConnection());
+    }
+
+    /**
+     * @test
+     */
+    public function authenticate_with_unsupported_preferred_kex_algorithm_failes(): void
+    {
+        $provider = SftpConnectionProvider::fromArray(
+            [
+                'host' => 'localhost',
+                'username' => 'foo',
+                'password' => 'pass',
+                'port' => 2223,
+                'preferredAlgorithms' => [
+                    'kex' => [self::KEX_ACCEPTED_BY_DEFAULT_OPENSSH_BUT_DISABLED_IN_EDDSA_ONLY],
+                ],
+            ]
+        );
+
+        $this->expectException(NoSupportedAlgorithmsException::class);
+        $provider->provideConnection();
+    }
+
     private function computeFingerPrint(string $publicKey): string
     {
         $content = explode(' ', $publicKey, 3);

test_files/sftp/sshd_custom_configs.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+
+cat <<'EOF' >> /etc/ssh/sshd_config
+
+KexAlgorithms curve25519-sha256
+Ciphers [email protected]
+MACs [email protected]
+HostKeyAlgorithms ssh-ed25519
+
+EOF